1. Field of the Invention
This invention relates to equipment used in a semiconductor fabrication process, and more particularly, to a photoresist dispense pump in a coater of a wafer track.
2. Description of Related Art
In the fabrication process of a semiconductor device, steps of performing photolithography processes are repeated for patterning various materials consisted of the semiconductor device. A photolithography process normally includes coating a photoresist layer on the material to be patterned, partially exposing the photoresist layer by using a pre-determined mask, and developing the exposed photoresist layer. In the foregoing process, the photoresist layer is dispensed on a pre-determined plane through a photoresist coater unit of a wafer track.
Generally, a wafer track includes a coater unit for coating photoresist, and a developer unit, wherein the coater unit further includes a photoresist dispense pump for dispensing photoresist. For a conventional wafer track, since the reloading rate of the photoresist dispense pump doesn't always catch the dispensing rate of the photoresist dispense pump during functioning, foam is then generated and stuck within the pump and filter. Hence, a poor coating, such as a photoresist layer contains radial traces caused by the popping of bubbles, or other problem, such as erosion on the inner surface of feeding pipe, happens. The photoresist consists of sensitizer, binder, and methyln n-amyl ketone (MAK), wherein MAK is about 60% to 80% of the photoresist. The vapor pressure of the MAK at a low temperature is relatively low, for example, the vapor pressure of MAK is about 2 to 3 mmHg at 20.degree. C. In the case that the dispensing rate of the photoresist dispense pump is faster than its loading rate during its repeatedly motion, there will be spaces of a lower vapor pressure or even vacuum generated within the the photoresist dispense pump. Hence, bubbles or foams are formed in the photoresist dispense pump.
FIG. 1 is a diagram that shows the photoresist-loading path of the photoresist dispense pump of a conventional wafer track. Referring to FIG. 1, photoresist is firstly transferred from a photoresist supply gallon bottle 10 toward the buffer tank by controlling the nitrogen gas filled into the photoresist supply gallon bottle tank 10. Then, photoresist is transferred into a bellows pump 14. By the repeated motion of the bellows pump 14, photoresist is again transferred to a filter 16. The filtered photoresist s transferred to a nozzle and dispensed out on a pre-determined plane. However, since the retrieving rate of the bellows pump 14 doesn't match the photoresist-reloading rate, the pressures inside and outside the bellows are different. The difference on the pressures inside and outside the bellows further leads the formation of foams and bubbles, and other problems.